Field of the Invention
The present invention relates to an optical apparatus for deforming the reflecting surface of a mirror, a projection optical system using the optical apparatus, an exposure apparatus, and a method of manufacturing an article.
Description of the Related Art
Since an astronomical telescope and an exposure apparatus used to manufacture a semiconductor device and the like are required to improve the resolution, it is necessary to accurately correct the optical aberration of an optical system used in these apparatuses. To achieve this, there are proposed optical apparatuses for correcting the optical aberration of an optical system by deforming the reflecting surface of a mirror included in the optical system (see patent literatures 1 and 2). Each of the optical apparatuses described in patent literatures 1 and 2 has a plurality of actuators each for applying a force to the rear surface (a surface opposite to the reflecting surface) of the mirror, and can correct the optical aberration of the optical system by controlling the driving of each actuator to deform the reflecting surface of the mirror.
If the mirror vibrates when the optical apparatus deforms the reflecting surface of the mirror, it may become difficult to accurately correct the optical aberration of the optical system. The optical apparatus is, therefore, required to support the mirror so that the eigen frequency of the mirror becomes high. In the optical apparatuses described in patent literatures 1 and 2, however, an actuator having low rigidity is used as each actuator for applying a force to the rear surface of the mirror, and the mirror can be supported at its peripheral portion by a supporting member. In the optical apparatuses described in patent literatures 1 and 2, therefore, it is difficult to support the mirror so that the eigen frequency of the mirror becomes high.
[Patent Literature 1] Japanese Patent Laid-Open No. 2005-4146
[Patent Literature 2] Japanese Patent Laid-Open No. 2004-64076